Line printers of the dot matrix type are typically comprised of a print head movable across a paper document and being capable of printing selected dot positions in a dot column. In one typical embodiment, the dot column has seven dot positions which may be selectively printed in any combination. Five adjacent dot columns typically comprise a single alphanumeric character or other symbol thereby creating a 5 .times. 7 dot matrix wherein the selected printing of the 35 possible dot positions cooperatively form the desired alphanumeric character or other symbol. The printer in its most general form, moves the print heat to the left-hand-most position of the paper document and advances the paper document in readiness for printing the next line (normally referred to as a carriage return-line feed) operation. The print head then moves across the paper document successively printing dot columns at selected positions along the line until it reaches the right-hand end of the paper document thereby completing a line of print. The print head is then moved in the reverse direction, typically at a speed faster than the printing speed, back to the start or left-hand-most position and the paper document is again advanced in readiness for printing the next line.
Numerous techniques and apparatus have been developed to increase printing speeds, one of which is the bidirectional printer which is capable of printing a line of print as the print head moves in either the forward or reverse direction. In operation, every other line of print is produced by moving the head in the forward direction and every intervening line of print is produced by moving the head in the reverse direction thereby eliminating the need for a carriage return operation so that only the paper document need be moved upon the completion of each line of print to advance the paper document in readiness for printing the next line.
The above technique constitutes the most efficient manner presently known for operating line printers in applications wherein the printed matter consists of a large number of lines with each line being substantially filled to capacity with alphanumeric characters and/or other symbols. However, a number of applications exist wherein the data field of a line of print occupies only a fractional portion of a line. With graphic formats of this type, the bidirectional printer nevertheless causes the print head to continue to move over the remainder of the line until it reaches the end of the paper document toward which it is moving, at which time it stops, reverses its direction, and prints the next line. If, for example, the next line of print likewise occupies a mere fraction of the entire length of the line, the movement of the print head over the remainder of the unprinted length of line and reversal of the print head over a significant portion of the next line of print before actually initiating printing becomes wasteful of printing time thereby resulting in a significant reduction in the printing speed of the printer.